A. Field of the Invention
This invention relates generally to the fields of dentistry and orthodontics. More particularly, the invention relates to methods for evaluating the areas of contact, and near contact, between upper and lower teeth when the upper and lower arches are in a closed or occluded condition. Knowledge of such areas of contact (“occlusal contacts” herein) is helpful in planning orthodontic treatment. The present invention provides methods of determining and displaying such occlusal contacts using a computer and three-dimensional virtual models of teeth.
B. Description of Related Art
In orthodontics, a patient suffering from a malocclusion is typically treated by bonding brackets to the surface of the patient's teeth. The brackets have slots for receiving an archwire. The bracket-archwire interaction governs forces applied to the teeth and defines the desired direction of tooth movement. Typically, the bends in the wire are made manually by the orthodontist. During the course of treatment, the movement of the teeth is monitored. Corrections to the bracket position and/or wire shape are made manually by the orthodontist.
The key to efficiency in treatment and maximum quality in results is a realistic simulation of the treatment process. Today's orthodontists have the possibility of taking plaster models of the upper and lower jaw, cutting the model into single tooth models and sticking these tooth models into a wax bed, lining them up in the desired position, the so-called set-up. This approach allows for reaching a perfect occlusion without any guessing. The next step is to bond a bracket at every tooth model. This would tell the orthodontist the geometry of the wire to run through the bracket slots to receive exactly this result. The next step involves the transfer of the bracket position to the original malocclusion model. To make sure that the brackets will be bonded at exactly this position at the real patient's teeth, small templates for every tooth would have to be fabricated that fit over the bracket and a relevant part of the tooth and allow for reliable placement of the bracket on the patient's teeth. To increase efficiency of the bonding process, another option would be to place each single bracket onto a model of the malocclusion and then fabricate one single transfer tray per jaw that covers all brackets and relevant portions of every tooth. Using such a transfer tray guarantees a very quick and yet precise bonding using indirect bonding.
However, it is obvious that such an approach requires an extreme amount of time and labor and thus is too costly, and this is the reason why it is not practiced widely. The normal orthodontist does not fabricate set-ups; he places the brackets directly on the patient's teeth to the best of his knowledge, uses an off-the-shelf wire and hopes for the best. There is no way to confirm whether the brackets are placed correctly; and misplacement of the bracket will change the direction and/or magnitude of the forces imparted on the teeth. While at the beginning of treatment things generally run well as all teeth start to move at least into the right direction, at the end of treatment a lot of time is lost by adaptations and corrections required due to the fact that the end result has not been properly planned at any point of time. For the orthodontist this is still preferable over the lab process described above, as the efforts for the lab process would still exceed the efforts that he has to put in during treatment. And the patient has no choice and does not know that treatment time could be significantly reduced if proper planning was done.
U.S. Pat. No. 5,431,562 to Andreiko et al. describes a computerized, appliance-driven approach to orthodontics. In this method, certain shape information of teeth is acquired. A uniplanar target archforrn is calculated from the shape information. The shape of customized bracket slots, the bracket base, and the shape of an orthodontic archwire, are calculated in accordance with a mathematically-derived target archform. The goal of the Andreiko et al. method is to give more predictability, standardization, and certainty to orthodontics by replacing the human element in orthodontic appliance design with a deterministic, mathematical computation of a target archform and appliance design. Hence the '562 patent teaches away from an interactive, computer-based system in which the orthodontist remains fully involved in patient diagnosis, appliance design, and treatment planning and monitoring.
More recently, in the late 1990's Align Technologies began offering transparent, removable aligning devices as a new treatment modality in orthodontics. In this system, a plaster model of the dentition of the patent is obtained by the orthodontist and shipped to a remote appliance manufacturing center, where it is scanned with a laser. A computer model of the dentition in a target situation is generated at the appliance manufacturing center and made available for viewing to the orthodontist over the Internet. The orthodontist indicates changes they wish to make to individual tooth positions. Later, another virtual model is provided over the Internet and the orthodontist reviews the revised model, and indicates any further changes. After several such iterations, the target situation is agreed upon. A series of removable aligning devices or shells are manufactured and delivered to the orthodontist. The shells, in theory, will move the patient's teeth to the desired or target position. Representative patents describing the Align process include U.S. Pat. Nos. 6,217,325; 6,210,162; and 6,227,850, which are incorporated by reference herein.
Other patents addressed to planning treatment for a patient include Doyle, U.S. Pat. No. 5,879,158, Wu et al., U.S. Pat. No. 5,338,198 and Snow et al., U.S. Pat. No. 6,068,482.
Orthodontics and dentistry involves the three-dimensional spatial positioning of teeth to get the best possible fit. Critical to the success is the relative position of the teeth within the arch and with the opposing arches. The determinants of these relationships is driven by both the location and shape/form of the teeth. Although teeth may be ideally localized spatially their fit may be poor because the shape of the teeth is improper. Determination of the fit between teeth can be best estimated by defining the contact points/areas between them. Therefore, if the teeth are located correctly and the contact points are not, it may be assumed there are discrepancies in the shape of the teeth. Location of these discrepancies is vital to achieve the desired occlusion.
Present approaches to defining or identifying these discrepancies are at best empirical. In current orthodontic and dental practice, occlusal contacts are determined by an orthodontist or dentist by using a color coated, thin plastic sheet known as “articulating paper”. The patient “bites” onto this foil, and the color is transferred onto the tooth surface, thus indicating where teeth have occlusal contact. This technique is contact-based and provides no quantitative data in terms of degree of poor fit.
In accordance with one aspect, the present invention provides for a simulation of this determination and display of occlusal contact using computer techniques and a virtual model of the patient's dentition. The determination and display of the occlusal contacts during treatment planning, prior to initiating treatment, allows for the orthodontist to better optimize the set-up on the computer. For example, the orthodontist may realize that the set up should be modified by moving one or more teeth relative to the opposing arch to provide for better occlusal contact or prevent a collision between teeth during movement of the teeth from initial to finish positions. Once this more optimal tooth set up has been determined, an appliance to move teeth to the desired positions can be designed and fabricated. The present invention is applicable to appliance systems generally and is not limited to a bracket and wire approach to straightening teeth.